This is a very good question and raises many interesting ideas.
There are some people who are spiritually 'switched on' and others who are spiritually dead. Some people simply feel nothing spiritual in their experience of life whatsoever, and no matter how hard they try they cannot find any special meaning or experience in anything religious or spiritual. This may be the result of their upbringing, or it could simply be the way they are. These people don't spend their time contemplating ideas of God, morality, salvation, divine guidance, etc. Therefore, they come in two forms: the satisfied theists, and the satisfied atheists. People who are born into a religious tradition, yet are spiritually dead or indifferent, often remain in that religious tradition simply because it feels normal and they accept it without much thought. They merely accept what is tought to them as children and don't think too hard about it. Others, because they don't find any value in spirituality, drift away from religion altogether because it either bores them, makes them uncomfortable or seems uncool.
There are others, however, who are very spiritually alive and aware. People who think constantly about God, faith, the afterlife, the meaning of life, morality, and other matters of philosophy and spirituality. These are the kind of people who convert. These are the spiritual thinkers, who think hard about matters of faith and work out independantly where they stand on certain theological issues. They are hungry for God, hungry for meaning, hungry for understanding and purpose and truth. Not all of them find it, many are misdirected and led, and find themselves converting to churches which might satisfy a certain need for those hungry searching individuals, but do not contain the fullness of Christ's Church on earth. Such people experience a very real spiritual hunger, and their search leads them to Protestantism, Catholicism, the Society of Friends, Islam, Buddhism, or whatever happens to satisfy the strongest aspects of their individual thirst. Others do find their way to the Church of Christ, and it is fortunate that they do. Others who are spiritually alive and spiritually conscious find the answers they are looking for right in front of them - such people are those born into the Church, and as they get older they appreciate it more and more.
Those who are spiritually alive find themselves asking, searching and thirsting. Many find what they are looking for in the Church they were raised in, others need to look elsewhere. Not all of them find the Truth, although their searches may be sincere nonetheless. Let us pray that all those who are genuinely thirsting for God may discover the Orthodox Church.
Personally, I discovered Orthodoxy after I had already found God and Christ. My searching and thirsting had been growing more intense with every day, and I felt myself drawn in a certain direction. When I finally fell down on my knees and prostrated before God the Father, the Son and the Holy Spirit, I still had not found Orthodoxy. I was considering becoming an Anglican. It was not long afterwards, however, that I learnt that the original Church of Christ is still alive and contains the spiritual fullness that I wanted in my Christian experience. I am glad that I found Orthodoxy, but had I not read certain books or looked at certain websites, or had I not studied early Christian history in high school, I very possibly could have become an Anglican or Quaker instead.